Reviewed by USGSAlaska87y ago
M7.0 earthquake 80 km SSE of Attu Station, Alaska
Tuesday, April 16, 1940, 06:07:47 UTC · 52.224°N, 173.778°E
A magnitude 7.0 earthquake struck 80 km SSE of Attu Station, Alaska on Tuesday, April 16, 1940, 06:07:47 UTC, at a depth of 30.0 km (shallow). It is the strongest earthquake within 300 km since an M7.2 on September 8, 1939.
- Magnitude
- 7.0
- Major · mw
- Depth
- 30 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 200 km aftershock search area
In context
How big was it, and why here?
Energy released
548 kilotons of TNT
That is about 36 times the Hiroshima bomb. It released about 1,148 times the energy of a magnitude 5.0.
Tectonic setting
75 km
from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
30 km
Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.
I felt it — report to USGS ↗USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.
After the main event
Aftershocks within 200 km
USGS lists 4 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M7.0 on April 16, 1940. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 23 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.993 km NW of Attu Station, AlaskaDecember 17, 1929 · 172 km NW of this epicenter
- 7.4151 km S of Attu Station, AlaskaSeptember 2, 1907 · 104 km SW of this epicenter
- 7.2238 km SSE of Attu Station, AlaskaSeptember 8, 1939 · 159 km SE of this epicenter
- 7.0167 km WSW of Attu Station, AlaskaApril 10, 1909 · 195 km W of this epicenter
- 6.8129 km SSE of Attu Station, AlaskaNovember 13, 1911 · 54 km S of this epicenter
- 6.895 km SE of Attu Station, AlaskaFebruary 22, 1935 · 34 km E of this epicenter
- 6.78 km SE of Attu Station, AlaskaOctober 18, 1912 · 72 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 3 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1909M7.8
Aleutian Islands
10 Apr 1909 · 87 km away
- 1929M7.8
Aleutian Islands: Near Islands
17 Dec 1929 · 158 km away
- 1898M7.6
Aleutian Islands: Near Islands
29 Jun 1898 · 124 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.